This invention relates to removing solids from aqueous solutions of xanthan gum polymers which contain bacterial cell bodies. It is particularly useful for clarifying such polymer solutions for use as water thickeners in aqueous fluids which are injected into subterranean reservoirs to displace oil.
Numerous procedures have been proposed for clarifying xanthan gum polymer solutions. U.S. Pat. No. 3,966,618 describes treating such solutions with protease enzymes which disintegrate the bacterial cellular debris into water-soluble compounds to an extent such that the polymer solution is clarified. U.S. Pat. No. 3,711,462 describes earlier treatments of such solutions by adding clay particles that are subsequently coagulated and filtered-out so that the cellular bodies are removed along with the coagulated clay particles. U.S. Pat. No. 3,729,460 describes reacting such a debris-containing polymer solution with alkaline materials, at a pH of from about 11.8 to 12.8, to effect a clarification of the solution.
The substantially complete enzymatic disintegration of the cellular bodies tends to convert them to proteinaceous materials which, because they are too finely divided to be removed by filtration, remain in the polymer solution and provide nutrients for bacteria capable of destroying the polymer. The prior non-enzymatic clarification procedures, such as adsorption on coagulated clay particles, or an alkaline treatment prior to a filtration step, tend to be too costly or too difficult for use in waterflooding an oil reservoir.